Extracellular levels of adenosine and its metabolites in the striatum of awake rats: inhibition of uptake and metabolism

Abstract

The level of purines in the striatum of awake, freely moving rats was studied using microdialysis. The calculated extracellular concentration of adenosine and its metabolites inosine and hypoxanthine was very high immediately after implantation of the dialysis probe but decreased within 24 h to a level which remained stable for two days. Using in vitro calibration to determine the relative recovery of the dialysis probes we estimated resting levels in the striatal extracellular space to be 40, 110 and 580 nM, respectively. Inhibition of adenosine deaminase by deoxycoformycin produced a significant 1.4-fold increase in extracellular adenosine levels and a fall in inosine and hypoxanthine. A combination of three uptake blockers (dipyridamole, lidoflazine and nitrobenzylthioinosine), caused a 4.5-fold increase in extracellular adenosine levels without any change in inosine or hypoxanthine levels. After uptake inhibition deoxycoformycin did not have any significant effect. The present results show that the microdialysis technique can be used to determine levels of purines in the extracellular fluid of defined brain regions in awake animals. The high levels recorded during the first several hours after implantation may be artefactually high and reflect trauma. The results also show that adenosine levels can be altered in vivo by inhibitors of adenosine transport and adenosine deaminase. The present results indicate that the physiological adenosine level in striatal extracellular space is in the range 40-460 nM.

Transcriptional modulation of TCR, Notch and Wnt signaling pathways in SEB-anergized CD4+ T cells

“…Enhanced cell surface expression of the receptor, which responds in the 100-1000 nM range of adenosine, could not only increase this response but might also permit signaling in response to basal adenosine levels, which are estimated to be in the 30-300 nM range. 47 Several mechanisms whereby cAMP can induce anergy are known and may be categorized based upon their dependency on PKA. In a PKA-independent pathway, cAMP can directly activate a Rap1 GEF known as Epac (exchange protein activated by cAMP), 48 which in turn is able to inhibit IL-2 production by inhibiting cRaf-1 in the Ras signaling cascade.…”

Sensing Positive versus Negative Reward Signals through Adenylyl Cyclase-Coupled GPCRs in Direct and Indirect Pathway Striatal Medium Spiny Neurons

“…In our D2ϩ MSN model, the fraction corresponding to the high-affinity D2R is assumed to be 30% of the total D2R population, which produces a good fit to experimental data as indicated in the following sections, and this number also falls into the range of the high affinity fraction estimated in vivo (Laruelle et al, 1997). The basal concentration of DA and Adn were set at 10 and 150 nM, respectively (Ballarín et al, 1991).…”

Variations of ATP and its metabolites in the hippocampus of rats subjected to pilocarpine-induced temporal lobe epilepsy

“…Microdialysis and HPLC assay of 1,N 6 -etheno-purines Our microdialysis protocol was adapted based on previous method described by Ballarin et al (1991) [15]. Briefly, the animals were anesthetized by intraperitoneal injection with a cocktail containing 67 and 13 mg/kg ketamine and xylazine, respectively, and immobilized in a stereotaxic device.…”